1. Field of the Invention
The present invention relates to a slidably bearing or low-friction vibration-isolating rubber member, and in particular to a self-lubricating vibration-isolating product suitably employed as a rubber bearing member in a connecting device, or a pivotal connector such as a rubber bushing in a vehicle suspension system. More particularly, the present invention is concerned with a stabilizer bushing for an automotive vehicle, which has excellent slidability, i.e., a relatively low bearing friction relative to a stabilizer bar engaging a bore formed therethrough, so as to enable a stabilizer device to function in a more effective manner, and which is considerably economical to manufacture. The invention further relates to a slidable annular eye bushing wherein a sleeve member and a shaft member are elastically connected such that the sleeve and shaft members are rotatable relative thereof, and in particular to techniques for effectively improving the slidably bearing characteristics of the eye bushing and reducing the cost of manufacture.
2. Discussion of the Prior Art
In a known connnecting device such as a ball joint, a rubber bearing is used as a vibration-isolating rubber member for absorbing vibrations and shocks applied to the connecting device. Such a rubber bearing is disclosed in examined Japanese Utility Model Application published under Publication No. 55-33059. Further, an annular vibration-isolating rubber bushing is used as a slidable vibration-isolating bushing in a pivotal connecting device disposed in a suspension system of a motor vehicle. Such a rubber bushing is disclosed in U.S. Pat. No. 3,331,642 and unexamined Japanese Utility Model Application published under Publication No. 59-153736. These rubber bearings and bushings, and other vibration-isolating rubber members are disposed between two members, such that the rubber member is slidable relative to at least one of the two members.
More specifically, a vibration-isolating rubber member used as stabilizer bushings for an automative vehicle, are well known in the art. The stabilizer bushings are employed for fixing a central portion of a generally U-shaped stabilizer bar to the body or suspension member of a vehicle, so as to permit a rotational movement of the stabilizer bar relative to the bushings. Usually, the stabilizer bushing is constituted by a generally annular elastic rubber body having an outer profile which consists of a generally U-shaped surface and a flat surface. The rubber body has a cylindrical bore which is formed in the axial direction through a substantially radially central portion thereof. The stabilizer bar engages the cylindrical bore and is thereby retained by the rubber body. On the other hand, the rubber body is attached to a suitable portion of the vehicle body or suspension member by a U-shaped metal retainer, which covers the U-shaped outer surface of the rubber body and which is fixed such that the flat outer surface of the rubber body is forced against the vehicle body or suspension member.
The stabilizer bar retained by the stabilizer bushings connects a left and a right suspension arms of the vehicle. When the suspension arms are displaced, a difference in the amount of displacements of the two arms is absorbed by elastic deformation or strain of the stabilizer baar, whereby the running stability of the vehicle is ensured. On the other hand, when the left and right suspension arms of the vehicle undergo substantially the same amount of displacement, the stabilizer bushings allow the stabilizer bar to rotate, thereby permitting the displacements of the suspension arms. Therefore, the stabilizer bushings are required to provide excellent slidability or a sufficiently low bearing friction, as well as high vibration-isolating characteristics.
Further, a vibration-isolating rubber member is also used as eye bushings provided at opposite ends of a leaf spring for suspension of a vehicle axle. Each eye bushing has a sleeve member generally called "spring eye" formed integral with the corresponding end portion of the leaf spring. The sleeve member is connected to a shaft member fixed to the vehicle body, via an annular elastic rubber member disposed therebetween.
This rubber member usually consists of a cylindrical portion having a suitable length, and at least one circumferential flange portion each extending from a corresponding end of the cylindrical portion in the radially outward direction. The sleeve member at each end of the leaf spring is fitted on the outer circumferential surface of the cylindrical portion of the rubber member, while the shafat member fixed to the vehicle body is inserted through a central bore formed in the rubber member. The shaft member is fixed to the vehicle body such that each flange portion of the rubber member is sandwiched between a collar member and the corresponding end face of the sleeve member. Thus, the rubber member is interposed between the sleeve and shaft members.
The rubber member of the eye bushing described above is required to elastically yield for attenuating transmission of vibrations from the vehicle axle via the leaf spring to the vehicle body, but also permits connection of the leaf spring to the vehicle body so that the leaf spring may be flexed, or so thata the sleeve member at the end of the leaf spring may be rotated relative to the fixed shaft member. In other words, the rubber member must have excellent rotational slidability or a self-lubricating property, as well as excellent vibration-isolating or spring characteristics.
However, the known rubber member used for the stabilizer or eye bushings, which is formed of a conventional ordinary rubber material, has a relatively high coefficient of friction, and therefore does not demonstrate sufficiently satisfactory slidably bearing characteristics or self-lubricating capability. Consequently, where the rubber member is used as the stabilizer bushings, the stabilizer bar does not effectively function to ensure required running stability of the vehicle. Where the rubber member is used as the eye bushings, the rubber member may adversely influence the spring characteristics of the leaf spring.
Techniques to solve the above inconveniences of the conventional slidable vibration-isolating rubber members have been proposed. For instance, the surface of the rubber member which engages the stabilizer bar, or sleeve or shaft member is covered with a liner of a fluorine-containing resin. Alternatively, a sliding member such as a sleeve made of an oil-impregnated resin is disposed between the stabilizer bar and the inner surface of the rubber member, or between the sleeve member of shaft member and the corresponding outer or inner surface of the rubber member. Although such a liner or sliding member is effective to increase the slidability of the vibration-isolating bushing, the additional use of the specially designed liner or sliding member will inherently increase the cost of manufacture of the bushing. Described more specifically, the material cost of the fluorine-containing resin liner is considerably expensive, and the step of applying the liner to the appropriate surface of the rubber member is also relatively costly. Thus, the bushing using the liner has a problem of its relatively high cost, as compared with the advanatage offered by the use of the liner. On the other hand, the sliding member made of an oil-impregnated resin requires additional parts or specific constructional modifications of the members concerned, in order to provide the sliding member in position between the rubber member and the mating component such as the stabilizer member or sleeve or shaft member. Further, the assembling of the bushing which includes the sliding member and those additional parts is time-consuming and accordingly costly.